1. Field of the Invention
The present invention relates to an armature and an electric motor having the same.
2. Description of Related Art
In an electric motor of, for example, a vehicular electric device, which is installed to a vehicle, an armature is rotatably supported by bearings in a yoke that has a plurality of magnets that form magnetic poles.
As an armature of such a motor, there has been proposed an armature, in which core sheets are stacked one after another to form a core and are fitted over a shaft such that the core has a plurality of generally identical T-shaped teeth and a tooth connecting portion for connecting the teeth together (see, for example, Japanese Unexamined Patent Publication No. 2001-298917A). In this armature, spaces, each of which is defined between adjacent teeth in cooperation with the tooth connecting portion, are formed as identically configured slots, and windings are wound at the slots.
The double-flyer winding method is known as a winding method for winding the windings around the above-described core from two locations, which are point symmetry about the rotational axis of the core. Specifically, this is the winding method of the following type. That is, an initial winding is placed and wound around two of the slots, which are spaced from each other by a predetermined number of teeth (or one tooth). This winding operation is executed at each of the two locations, which are point symmetry about the rotational axis of the core. Thereafter, the subject slots are sequentially changed to the adjacent ones, and the windings are wound at the subject slots in the same manner.
In the above described winding method, as shown in FIG. 12, a gap 56 may be left at a core 50 center side in each of particular slots 53b, 53g, each of which is placed at a circumferential intermediate part of a first winding (initial winding) 55a located between two circumferential ends of the first winding 25a. 
That is, as indicated by dotted lines in FIG. 12, the first winding 55a has been already wound at the slot 53b, 53g located at the circumferential intermediated part of the first winding 55a and covers a radially inner part of the slot 53b, 53g by the time of winding the second winding 55b after the first winding 55a. Therefore, when the second winding 55b is wound, the gap 56 may be created at the core 50 center side in the slot 53b, 53g. 
Therefore, the position of the second winding 55b, which is wound at the location on the core 50 outer peripheral side of the gap 56 in the radial direction of the core 50, as well as the position of the other winding 55e, which is wound at the location on the core 50 outer peripheral side of the second winding 55b in the radial direction of the core 50, become unstable. Furthermore, these unstable positions and states of the windings will have substantial influences on the positions and states of the subsequently wound windings. Therefore, the rotational unbalance of the armature of the motor disadvantageously occurs.
The unbalance of the armature, which is created in the winding process of the armature, may be corrected in the following balance correcting process. In the balance correcting process, a degree of dynamic unbalance of the armature is measured. When it is determined that the measured degree of the dynamic unbalance is out of the standard, the balance of the armature may be improved through subtractive or additive correction. Here, in the subtractive correction, a portion of the core, which causes the unbalance, is removed by cutting a required amount of the material therefrom through use of a cutter or a laser machine. In contrast, in the additive correction, a required additional weight is added to a portion of the winding or slot, which causes the unbalance, by applying, for example, putty thereto. These corrections require the dedicated process or dedicated facility, so that the manufacturing costs are disadvantageously increased. Also, the motor efficiency may possibly be deteriorated.
If it is possible to reduce the number of the unbalanced products, the above described balance correcting process may possibly be eliminated. However, the various factors influence the unbalancing of the armature in the winding process where the large number of the unbalanced products is generated. In order to reduce the unbalancing, it has been proposed to wind the windings to the core having the even number of the slots such that the windings are symmetrically placed on the left side and the right side of the core. However, even in this way, it is difficult to reduce the unbalancing by coinciding the states of the windings on the left side and the right side of the core.
According to a previously proposed technique, an insulator is provided to electrically insulate the windings from the metal core. The insulator is press fitted over the surface of the core to electrically insulate the windings from the metal core.
However, a gap may be disadvantageously created between the insulator and the core. Furthermore, when the windings are wound at the slots upon fitting of the insulator to the core, a portion of the insulator may possibly be deformed by a tension of the windings. As discussed above, it has been demanded to provide a technique, which limits the occurrence of the deformation or misalignment caused by the tension at the time of winding the windings.